In foodstuff, flavors are very important components and characterize foods; however, the flavors are components more likely to deteriorate with time by various causations during processing, distribution and storage. There are a variety of causations for deteriorating flavor components, and flavor components are likely to drastically deteriorate by the influence of heat, oxygen, light or the like in a processing step such as sterilization, and in each stage of distribution, storage, selling or the like of foodstuff, and further causing off flavor, thereby leading to a lowering of its quality. Furthermore, due to widespread in packaging of beverages in transparent or semi-transparent plastic vessels and foods in transparent bags, selling in showcases in convenience stores, and the like in recent years, chances of exposure of foodstuff to light have been dramatically increased, thereby giving more situations where the flavors are more likely to be deteriorated due to light. Especially, it has been known that citrus beverages, foodstuff containing lacto components and the like show drastic deterioration of flavors under irradiation with light. There are more likely to have situations to be influenced by heat, oxygen or the like because of selling foodstuff packaged in a vessel having a high oxygen permeability at a high temperature such as selling of foodstuff packaged in a warmed plastic vessel.
It has been known that flavors for foodstuff such as citrus flavors, coffee-based flavors, and milk-based flavors are influenced by heat, oxygen, light or the like, thereby causing deterioration with time, such as change in flavor components and generation of off flavor. Natural flavors and those similar to natural flavors especially are likely to have the tendency.
In order to solve this, various studies have been made on sterilization in a short period of time, distribution at a low temperature, development of a functional vessel having UV absorbability, addition of an antioxidant and the like. Among them, as to the addition of an antioxidant, there has been used from long ago synthetic antioxidants such as dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), and propyl gallate. However, in recent years, there has been pointed out that these antioxidants impart an influence undesirable for physical health of human bodies, and the use of these antioxidants is avoided. In view of the above, antioxidants and deterioration preventives for flavor, which are derived from natural products substituting these synthetic antioxidants have been desired, and various proposals have been made. For example, there have been proposed a method of preventing deterioration of flavors in foodstuff utilizing chlorogenic acid, coffeic acid or the like extracted from green coffee beans [see, for example, Japanese Patent Laid-Open (JP-A) Nos. Hei 4-27374 (pages 3 to 5), Hei 6-38723 (pages 2 to 7)]; a combined use of ferulic acid and proanthocyanidin [see, for example, JP-A No. 6-38723 (pages 2 to 7)]; a method of preventing deterioration of a water-soluble flavor composition utilizing an enzyme-treated rutin [see, for example, JP-A No. 4-36395 (pages 2 to 5)] and the like. However, many of these deterioration preventives have to be used in a large amount for obtaining the effect, so that there is a disadvantage that the tastes of the deterioration preventives themselves give bad influence to the flavors of foodstuff. Especially, ferulic acid has undesirable tastes such as fermented odor, rice bran odor or astringency derived from its origin. In addition, since many of these deterioration preventives are water-soluble, there is also a disadvantage that satisfactory effects are not obtained in an emulsion flavor prepared by emulsifying or solubilizing an oily flavor, while a water-soluble flavor using ethanol as a solvent has some effects. Therefore, there is a significant limitation on its utilization in food application. In addition, as to ferulic acid, its crystallinity is also a hindrance on its utilization. Since ferulic acid added to beverages or foods forms crystals during storage, the commercial values of a product added therewith are lost, so that ferulic acid has an effect as an antioxidant but ferulic acid has not yet been actually used under current situations.
Those widely used for oxidation prevention of oily foods are dl-α-tocopherol and extracted tocopherol. While there are numerous literatures and the like reporting oxidation prevention by tocopherol against oil using an index of POV or COV, there are few reports on deterioration prevention of a flavor component when used together with a water-soluble antioxidant, and the effect of preventing deterioration for a flavor component when used alone is actually weak under current conditions. In addition, oily antioxidants such as tocopherol are generally required to be in the form of oil-in-water or -polyhydric alcohol emulsions when used for water-based foods. However, there are also some disadvantages that emulsification thereof is unstable in water or a polyhydric alcohol, and influenced by a flavor component, a flavonoid, a catechin or the like, thereby causing separation of tocopherol, and impairing the appearance of foods, and the like. As described above, there are various processes for a flavor deterioration preventive; however, there are little means having a satisfactory effect and usefulness. Therefore, further developments have been desired.